Adoption was a procedure, often legal but sometimes informal, by which a person or persons took an orphaned or abandoned child in and raised them as their own. Informally term applied to the acquisition of both objects (i.e. a pet) or places (i.e. a colony) as adoption.
During their childhood, Rom's brother Quark told everyone he was adopted in order to explain the younger boy's small lobes. He recounted this to Martus Mazur in 2370, but the El-Aurian wasn't interested. (DS9: "Rivals")